.TH DCB-REWR 8 "15 may 2023" "iproute2" "Linux"
.SH NAME
dcb-rewr \- show / manipulate the rewrite table of
the DCB (Data Center Bridging) subsystem
.SH SYNOPSIS
.sp
.ad l
.in +8

.ti -8
.B dcb
.RI "[ " OPTIONS " ] "
.B rewr
.RI "{ " COMMAND " | " help " }"
.sp

.ti -8
.B dcb rewr " { " show " | " flush " } " dev
.RI DEV
.RB "[ " prio-dscp " ]"
.RB "[ " prio-pcp " ]"

.ti -8
.B dcb rewr " { " add " | " del " | " replace " } " dev
.RI DEV
.RB "[ " prio-dscp " " \fIDSCP-MAP\fB " ]"
.RB "[ " prio-pcp " " \fIPCP-MAP\fB " ]"

.ti -8
.IR DSCP-MAP " := [ " DSCP-MAP " ] " DSCP-MAPPING

.ti -8
.IR DSCP-MAPPING " := " \fIPRIO \fB:\fR "{ " DSCP " | " \fBall\fR " }"

.ti -8
.IR PCP-MAP " := [ " PCP-MAP " ] " PCP-MAPPING

.ti -8
.IR PCP-MAPPING " := " \fIPRIO \fB:\fR PCP\fR

.ti -8
.IR DSCP " := { " \fB0\fR " .. " \fB63\fR " }"

.ti -8
.IR PCP " := { " \fB0(nd/de)\fR " .. " \fB7(nd/de)\fR " }"

.ti -8
.IR PRIO " := { " \fB0\fR " .. " \fB7\fR " }"

.SH DESCRIPTION

.B dcb rewr
is used to configure the rewrite table, in the DCB (Data Center Bridging)
subsystem.  The rewrite table is used to rewrite certain values in the packet
headers, based on packet priority.

DCB rewrite entries are, like DCB APP entries, 3-tuples of selector, protocol
ID, and priority. Selector is an enumeration that picks one of the
prioritization namespaces. Currently, only the DSCP and PCP selector namespaces
are supported by dcb rewr.

The rewrite table is a list of DCB rewrite rules, that applies to packets
with matching priority.  Notably, it is valid to have conflicting rewrite
assignment for the same selector and priority. For example, the set of two
rewrite entries (DSCP, 10, 1) and (DSCP, 11, 1), where packets with priority 1
should have its DSCP value rewritten to both 10 and 11, form a well-defined
rewrite table.
.B dcb rewr
tool allows low-level management of the rewrite table by adding and deleting
individual rewrite 3-tuples through
.B add
and
.B del
commands. On the other hand, the command
.B replace
does what one would typically want in this situation--first adds the new
configuration, and then removes the obsolete one, so that only one
rewrite rule is in effect for a given selector and priority.

.SH COMMANDS

.TP
.B show
Display all entries with a given selector. When no selector is given, shows all
rewrite table entries categorized per selector.

.TP
.B flush
Remove all entries with a given selector. When no selector is given, removes all
rewrite table entries.

.TP
.B add
.TQ
.B del
Add and, respectively, remove individual rewrite 3-tuples to and from the DCB
rewrite table.

.TP
.B replace
Take the list of entries mentioned as parameter, and add those that are not
present in the rewrite table yet. Then remove those entries, whose selector and
priority have been mentioned as parameter, but not with the exact same
protocol ID. This has the effect of, for the given selector and priority,
causing that the table only contains the protocol ID (or ID's) given as
parameter.

.SH PARAMETERS

The following table shows parameters in a way that they would be used with
\fBadd\fR, \fBdel\fR and \fBreplace\fR commands. For \fBshow\fR and
\fBflush\fR, the parameter name is to be used as a simple keyword without
further arguments.

.TP
.B prio-dscp \fIDSCP-MAP
\fIDSCP-MAP\fR uses the array parameter syntax, see
.BR dcb (8)
for details. Keys are priorities, values are DSCP points for traffic
with matching priority. DSCP points can be written either directly as numeric
values, or using symbolic names specified in
.B /etc/iproute2/rt_dsfield
(however note that the file specifies full 8-bit dsfield values, whereas
.B dcb rewr
will only use the higher six bits).
.B dcb rewr show
will similarly format DSCP values as symbolic names if possible. The
command line option
.B -N
turns the show translation off.

.TP
.B prio-pcp \fIPCP-MAP
\fIPCP-MAP\fR uses the array parameter syntax, see
.BR dcb (8)
for details. Keys are priorities. Values are PCP/DEI for traffic with
matching priority. PCP/DEI values are written as a combination of numeric- and
symbolic values, to accommodate for both. PCP always in numeric form e.g 0 ..
7 and DEI in symbolic form e.g 'de' (drop-eligible), indicating that the DEI
bit is 1 or 'nd' (not-drop-eligible), indicating that the DEI bit is 0.  In
combination 1:2de translates to a mapping of priority 1 to PCP=2 and DEI=1.

.SH EXAMPLE & USAGE

Add a rule to rewrite DSCP to 0, 24 and 48 for traffic with priority 0, 3 and
6, respectively:
.P
# dcb rewr add dev eth0 prio-dscp 0:0 3:24 6:48

Add a rule to rewrite DSCP to 25 for traffic with priority 3:
.P
# dcb rewr add dev eth0 prio-dscp 3:25
.br
# dcb rewr show dev eth0 prio-dscp
.br
prio-dscp 0:0 3:CS3 3:25 6:CS6
.br
# dcb -N rewr show dev eth0 prio-dscp
.br
prio-dscp 0:0 3:24 3:25 6:48

Reconfigure the table so that only one rule exists for rewriting traffic with
priority 3.

.P
# dcb rewr replace dev eth0 prio-dscp 3:26
.br
# dcb rewr -N show dev eth0 prio-dscp
.br
prio-dscp 0:0 3:26 6:48

Flush all DSCP rules:

.P
# dcb rewr flush dev eth0 prio-dscp
.br
# dcb rewr show dev eth0 prio-dscp
.br
(nothing)

Add a rule to rewrite PCP to 1 and DEI to 0 for traffic with priority 1 and a
rule to rewrite PCP to 2 and DEI to 1 for traffic with priority 2:

.P
# dcb rewr add dev eth0 prio-pcp 1:1nd 2:2de
.br
# dcb rewr show dev eth0 prio-pcp
.br
prio-pcp 1:1nd 2:2de

.SH EXIT STATUS
Exit status is 0 if command was successful or a positive integer upon failure.

.SH SEE ALSO
.BR dcb (8)
.BR dcb-app (8)
.BR dcb-apptrust (8)

.SH REPORTING BUGS
Report any bugs to the Network Developers mailing list
.B <netdev@vger.kernel.org>
where the development and maintenance is primarily done.  You do not have to be
subscribed to the list to send a message there.

.SH AUTHOR
Daniel Machon <daniel.machon@microchip.com>
